The present invention relates to a packaging substrate and a manufacturing method thereof, an integrated circuit device and a manufacturing method thereof, and an SAW device, in particular to a technique effectively applicable to the packaging substrate on which an integrated circuit element is mounted by flip-chip bonding, a technique effectively applicable to the integrated circuit device that an integrated circuit element is hermetically sealed on the packaging substrate, a technique effectively applicable to the integrated circuit device that an integrated circuit element and the packaging substrate are coupled with each other by ultrasonic sound, and a technique effectively applicable to the SAW device which has a pair of resonators each having a shape of the teeth of a comb.
In the integrated circuit device that an integrated circuit element is mounted on the packaging substrate, a flip-chip method is considered as one of mounting methods thereof. In the flip-chip method, projecting electrodes are formed on element electrodes of the integrated circuit element, and then the projecting electrodes are directly coupled to substrate electrodes formed on a packaging substrate. Further, a wire-bonding method is also considered as another one of the mounting methods thereof. In the wire-bonding method, the integrated circuit element is coupled to the packaging substrate, and then the element electrodes of the integrated circuit element and the substrate electrodes of the packaging substrate are coupled to each other through wires.
Herein, in the wire-bonding method that a wire-bonding is carried out by the use of gold (Au) wiring, aluminum (Al) wiring, or the like, the substrate electrodes formed on the packaging substrate, in particular on the packaging substrate of ceramics, are formed by printing a conductive material on a surface of the packaging substrate. Subsequently, roughness of the surfaces of the substrate electrodes reflects diameters of particles of the conductive material constituting the substrate electrodes or materials of the packaging substrate, namely, roughness of substrate members, as it stands.
In the wire-bonding method, since the integrated circuit element is coupled to the packaging substrate, as mentioned above, junction portions in the substrate electrodes of the packaging substrate to be bonded to the wires are not such portions to which stress is structurally applied, when mechanical impact, vibrations, or thermal impact are applied to a whole of the device. Consequently, reliability of junction of the junction portions is generally estimated by a wire-pull test.
Generally, pull-strength in the wire-pull test is approximately between 5 g and 40 g. In addition, destroy is caused to occur not by a break in the junction portions between the wires and the substrate electrodes but by a break of the wires. In view of these, it is necessary that the junction portions have strength larger than breaking strength of the wires in the wire-bonding method. As a result, it becomes necessary that the junction of the substrate electrodes formed on the packaging substrate is not destroyed by a strength not larger than the breaking strength of the wires. Besides, in the above-mentioned flip-chip method; roughness of the surfaces of the substrate electrodes of the packaging substrate is similar to that in the wire-bonding method. Accordingly, any attention has not been paid to decision of the roughness in the flip-chip method.
In a case that a color of the substrate members is white, like an LTCC (Low Temperature Cofired Ceramics) substrate, reproducibility cannot be obtained in the conductive patterns of the substrate electrode portions due to roughness of a surface of each substrate electrode. It is therefore difficult that a position of the substrate electrode with respect to the substrate members is optically recognized. On the other hand, in the flip-chip method that the integrated circuit element and the packaging substrate are coupled to each other by the projecting electrodes, requirements for junction strength are different from those of the wire-bonding method.
Namely, in the flip-chip method, since the integrated circuit element and the packaging substrate are coupled to each other by the projecting electrodes, stress caused by the mechanical impact or vibrations is concentrated on the projecting electrodes. As a result, reliability of junction depends on junction strength between the projecting electrodes and the substrate electrodes. Herein, reliability of junction portions between the projecting electrodes and the substrate electrodes can be estimated by a die-share test.
On the other hand, in recent years, a mobile communication terminal equipment, such as a portable telephone, and the like has been rapidly progressed. From the viewpoint of convenience of portability or handiness, it is strongly desired that the mobile communication terminal equipment is not only small in size but also light in weight. In order to fabricate such a small and a light terminal equipment, it is essentially required that an electronic part or device used therein is also small in size and light in weight. Under the circumstances, many SAW elements, each of which has advantage for being fabricated small and light and each of in which a plurality of SAW resonators are formed in a piezo-electric substrate, have been used in a high-frequency section and an intermediate-frequency section of the terminal equipment.
An insertion loss and attenuation outside the pass band can be pointed out as important characteristics required for the SAW element, when the SAW element is used as a filter. Herein, the insertion loss influences power consumption of the mobile communication terminal equipment including the SAW element. The insertion loss becomes lower, the life of a battery included in the mobile communication terminal equipment becomes longer. Therefore, a capacity of the battery can be reduced, dependent on the insertion loss. Accordingly, the mobile communication terminal equipment can be fabricated small in size and light in weight, when the insertion loss can be low. Further, when wide range attenuation outside the pass band can be obtained in a filter, the mobile communication terminal equipment can also be fabricated small in size and light in weight.
Herein, the SAW element used in the SAW device has a pair of exciting electrode portions each of which has a shape of the teeth of a comb and which are formed on a piezo-electric substrate with being involved in each other. With the structure, in the SAW element, an electric field generated by applying voltage between the exciting electrode portions produces a surface acoustic wave (SAW) on the piezo-electric substrate. On the other hand, a produced surface acoustic wave (SAW) is converted into an electric signal by the exciting electrode portions also in the SAW element. In the SAW device having such an SAW element, adhesive are painted circularly on an area to be adhered to a cap. As a result, the adhesive are also painted not only on the substrate electrodes but also on a surface of the packaging substrate in which the substrate electrodes are not formed.
Herein, although the adhesive of resin can be adhered to the packaging substrate of ceramics itself with a large adhering strength, the adhesive of resin cannot be adhered to a metal, such as a plating layer, a substrate electrode, or the like with such a large adhering strength. Therefore, the cap adhered to the packaging substrate by the adhesive can be adhered at a sufficiently large strength to a portion in which the substrate electrodes are not formed. However, the cap adhered to the packaging substrate by the adhesive cannot be adhered at a desirable strength to a portion in which the substrate electrodes are formed. As a result, water invades from a portion between the substrate electrodes and the adhesive into the SAW device. Accordingly, reliability as the SAW device is so damaged. This problem is caused to occur not only in the SAW device but also in every integrated circuit device that an integrated circuit element is mounted on a packaging substrate.
Further, in such an SAW device, a packaging substrate on which an SAW element is mounted by the flip-chip method is not made of resin but mainly made of ceramics, such as alumina, LTCC, or the like, that is harder than the resin. Under the circumstances, in order to achieve fabrication of the SAW device that is small in size, light in weight, and low in cost, it is desirable that the packaging substrate is made of resin. However, if the packaging substrate is made of resin softer than the ceramics, the packaging substrate is inevitably bended while ultrasonic wave vibration is applied thereon in the flip-chip mounting. As a result, the ultrasonic wave power is not applied sufficiently on a surface by which the projecting electrodes and the packaging substrate are kept in contact with each other. Consequently, it becomes difficult that a necessary share strength is achieved. This problem is also caused to occur not only in the SAW device but also in every integrated circuit device that an integrated circuit element is mounted on a packaging substrate by the flip-chip method.
On the other hand, assuming that the SAW device is used within a mobile communication terminal, the SAW device meets some requirements. It is required for the SAW device that contact of the SAW element with the packaging substrate is maintained, even if the SAW device has been dropped from a height of 2 m. Herein, the height of 2 m is decided by adding a predetermined margin to a height by which a general user uses the mobile communication terminal.
In the interim, it is enough to enlarge area of the bumps as large as possible in order to achieve the above-mentioned performance of junction, in a case that the SAW element is flip-chip mounted in the packaging substrate by bumps. Subsequently, in order to enlarge the area of the bumps, it becomes inevitably necessary to enlarge area of a piezo-electric substrate constituting the SAW element. However, it is difficult to enlarge the area of the piezo-electric substrate, from the view point of requirements for making the terminal equipment small in size and light in weight. As a result, it is not possible that only the area of the bumps is merely enlarged.